CN103534785A - Lamp with phosphor composition for improved lumen performance, and method for making same - Google Patents

Abstract

This invention discloses a lamp comprising a radiation source and a phosphor dopant configured for radiation conversion, the phosphor dopant comprising at least two different rare-earth phosphors, wherein the phosphor dopant comprises at least one multi-peak rare-earth phosphor. The disclosed advantages may include a greater lumen output compared to the same lamp in which the phosphor dopant at the same fill weight does not contain at least one multi-peak rare-earth phosphor.

Description

Lamp with phosphor composition for improved lumen performance and method of preparation

Cross References to Related Applications

This application is a non-provisional patent application claiming priority under 35 U.S.C. 119(e) to previously filed co-pending provisional application Serial No. 61/485720, filed May 13, 2011, filed as This specification is incorporated by reference in its entirety.

technical field

The present invention relates generally to lamps employing phosphors for radiation conversion, and in particular to lamps having phosphor particles of a defined size distribution enabling improved lumen performance.

Background technique

Lamps with good energy efficiency, such as low-pressure discharge lamps (eg fluorescent lamps) are generally known. In such lamps, a phosphor layer is employed to convert the UV radiation into visible light. In order to obtain good color properties for visible light, one or more rare earth activated phosphors are usually employed in this layer. However, recent trends have increased the cost of rare earth activated phosphors. This has created a need to improve the lumen performance of fluorescent lamps relative to the amount of phosphor coating used in the lamp.

In some known fluorescent lamps, relatively coarse rare earth phosphor particle systems have been used to obtain higher lumens. However, when doing so, more phosphor needs to be used (ie high coat weight) to obtain a thick enough layer of phosphor coating to absorb all available UV energy.

Therefore, there is a need to avoid high Coat weight.

Contents of the invention

One embodiment of the invention relates to a lamp comprising a radiation source capable of emitting electromagnetic radiation of a first wavelength, and a phosphor configured in combination with said radiation source for converting said electromagnetic radiation into a second wavelength blend. The phosphor blend comprises at least two different rare earth phosphors, wherein the phosphor blend comprises at least one multimodal rare earth phosphor.

Further, the at least one multimodal rare earth phosphor comprises a first population of relatively coarse particles and a second population of relatively fine particles.

Further, the first group accounts for about 20 to about 80 wt % of the at least one multimodal rare earth phosphor, and the second group accounts for about 80 to about 80 wt % of the at least one multimodal rare earth phosphor. About 20 wt%.

Further, the multimodal rare earth phosphor comprises a bimodal particle distribution having a first maximum corresponding to relatively coarse particles having a _d50 less than or equal to about 10 microns, and a maximum corresponding to _ad50 Second maximum for relatively finer particles greater than or equal to about 1 micron.

Further, the blend comprises two or more different multimodal rare earth phosphors.

Further, the blend comprises at least three different rare earth phosphors.

Further, the blend further comprises at least one halogenated phosphor.

Further, the lamp achieves greater lumens than the same lamp at equal phosphor coat weights in which the blend does not contain at least one multimodal rare earth phosphor.

Further, the at least one multimodal rare earth phosphor comprises a plurality of particles, wherein at least some of the relatively finer particles are sized to fit in the interstices between at least some of the relatively coarser particles.

Further, the blend comprises a multimodal rare earth phosphor emitting red light.

Further, the rare-earth phosphor emitting red light includes one or more of europium-doped yttrium oxide, europium-doped yttrium vanadium phosphate, or metal pentaborate co-activated by manganese and cerium.

Further, the blend contains a multimodal rare earth phosphor emitting green light.

Further, the rare earth phosphors emitting green light include lanthanum phosphate co-activated by cerium and terbium, barium magnesium aluminate co-activated by europium and manganese, gadolinium magnesium pentaborate co-activated by cerium and terbium, or co-activated by cerium and terbium. One or more of magnesium aluminates.

Further, the blend contains multimodal rare earth phosphors emitting blue light.

Further, the blue-emitting rare earth phosphors include europium-doped halophosphate, europium-doped barium magnesium aluminate, europium-manganese co-activated barium magnesium aluminate, europium-doped strontium aluminate, doped One or more of europium borophosphate, cerium doped yttrium aluminate, or SECA.

Further, the lamp comprises 1 mg/cm ² to about 6 mg/cm ² of the phosphor blend.

Further, the radiation source includes one or more of a discharge-based radiation source or a solid-state radiation source.

Further, the first wavelength is in the blue or UV region of the electromagnetic spectrum, and the second wavelength is in the visible region of the electromagnetic spectrum and is longer than the first wavelength.

Another embodiment of the invention relates to a low-pressure discharge lamp comprising: at least one light-transmissive envelope; a filling gas composition capable of maintaining a hermetic seal within said at least one light-transmissive envelope. an electric discharge; a phosphor blend; and optionally one or more electrical leads disposed at least partially within the at least one light-transmissive envelope for providing current. The phosphor blend comprises at least two different rare earth phosphors, wherein the phosphor blend comprises at least one multimodal rare earth phosphor.

Another embodiment of the invention relates to a low-pressure discharge lamp comprising at least one light-transmissive envelope; a filling gas composition capable of maintaining a discharge sealed within said at least one light-transmissive envelope; and phosphorescence a phosphor blend; wherein the phosphor blend comprises at least two different rare earth phosphors, wherein the phosphor blend comprises at least one multimodal rare earth phosphor.

Yet another embodiment of the present invention is directed to a method comprising the step of combining a radiation source capable of emitting electromagnetic radiation at a first wavelength with a phosphor blend to convert said electromagnetic radiation to a second wavelength; wherein, The phosphor blend comprises at least two different rare earth phosphors, and wherein the phosphor blend comprises at least one multimodal rare earth phosphor; wherein the method operates the lamp to A consistent lumen output is obtained with the phosphor, and/or the method operates the lamp to obtain a higher lumen output at a constant amount of phosphor.

Other features and advantages of the present invention will be better understood from the following detailed description.

Description of drawings

Embodiments of the present invention will be described in more detail with reference to the accompanying drawings.

Fig. 1 shows schematically and in section a fluorescent lamp according to an embodiment of the present disclosure.

Detailed ways

According to an embodiment of the present invention, there is provided a lamp using a phosphor blend comprising a plurality of phosphors, wherein one or more of the phosphors is composed of two or more phosphor particles of separate particle size distributions ( such as coarse particles and fine particles). This can result in a more optimized amount of lumens relative to the amount of phosphor coating used.

As stated, embodiments of the present invention relate to a lamp comprising a radiation source capable of emitting electromagnetic radiation of a first wavelength, and configured in combination with said radiation source for converting said electromagnetic radiation to a second wavelength phosphor blends. The phosphor blend comprises at least two different rare earth phosphors, at least one of the at least two different rare earth phosphors being a multimodal rare earth phosphor. Typically, the first wavelength may be in the blue or UV region of the electromagnetic spectrum. Typically, the second wavelength may be in the visible region of the electromagnetic spectrum and be longer than the first wavelength.

As is generally known, a "phosphor" is one that absorbs radiant energy in one part of the electromagnetic spectrum and emits energy in another part of the electromagnetic spectrum. An important class of phosphors are crystalline inorganic compounds of high chemical purity and controlled composition, to which small amounts of other elements (called "activators") have been added to convert them into efficient fluorescent materials. Phosphors have been used in low pressure (eg, mercury vapor) discharge lamps to convert ultraviolet ("UV") radiation emitted by excited mercury vapor into visible light.

A "multimodal rare earth phosphor" is a phosphor activated by at least one rare earth element comprising particles with a multimodal particle size distribution. In some embodiments, the blend may comprise at least three (e.g., 3, 4, 5, 6) different rare earth phosphors, at least one of which is multimodal according to embodiments of the present specification of. In some embodiments, the blend may contain no more than two, preferably only one, multimodal rare earth phosphors. In some embodiments, all of the different rare earth phosphors may emit light of different colors (e.g., red, green, and blue); alternatively, there may be light emitting in the same or similar colors (e.g., two reds) in a blend. Two or more rare earth phosphors, and optionally, phosphors of different colors (eg, green and blue). In some embodiments, the blend may also include at least one non-rare earth phosphor, such as a halophosphor (eg, a non-rare earth activated metal halophosphate). For some applications (e.g. CFL lamps at relatively low color temperatures), there may be one rare earth phosphor (e.g. red) and one rare earth phosphor of a different color (e.g. green), at least one of these rare earth phosphors The latter are characterized as multimodal.

As used herein, a "multimodal" particle size distribution is intended to encompass bimodal particle sizes, as well as trimodal or other multimodal particle size distributions. Multimodal (eg, bimodal) particle size distributions can be determined by standard analytical methods well known to those of ordinary skill in the art. Alternatively, a multimodal particle size distribution can also refer to a mixture of particles that have been formulated to have more than one mode. For example, combining a powder with a single mode with another powder of the same phosphor type but with a different single mode can produce a bimodal particle size distribution (PSD), even though the maximum value of the PSD of the combined powder is difficult to analytically distinguish.

In certain embodiments, the multimodal rare earth phosphor of the blend may comprise rare earth phosphor particles having a bimodal particle size distribution. Thus, the at least one multimodal rare earth phosphor of the blend may comprise a first population of relatively coarser particles and a second population of relatively finer particles. Typically, the first population (of relatively coarser particles) may comprise from about 20 wt% to about 80 wt% (more narrowly, from about 33 wt% to about 67 wt%) of the at least one multimodal rare earth phosphor; and ( The second population of relatively finer particles may comprise from about 80 wt% to about 20 wt% (more narrowly, from about 67 wt% to about 33 wt%) of the at least one multimodal rare earth phosphor.

According to an embodiment of the present invention, when the blend comprises rare earth phosphor particles having a bimodal particle size distribution, the bimodal particle size distribution may have a relative density corresponding to a _d50 of less than or equal to about 10 μm (eg, about 5 μm to about 10 μm). Coarse particles may have a first maximum and may have a second maximum corresponding to relatively finer particles having _ad50 greater than or equal to about 1 μm (eg, about 1 μm to about 6 μm). In some narrower embodiments, the relatively coarser particles in the bimodal particle size distribution may have a d ₅₀ of less than or equal to about 8 μm (e.g., about 5 μm to about 8 μm), and the relatively finer particles have a d50 of greater than or equal to about 8 μm. Ad ₅₀ of 2 μm (eg, about 2 μm to about 6 μm). Typically, at least one multimodal rare earth phosphor in the blend may comprise particles having an overall average size in the range of about 2 to about 10 μm.

Without being bound by theory, at least one multimodal rare earth phosphor comprises a plurality of particles, wherein at least some of the relatively finer particles are sized to fit in the interstices between at least some of the relatively coarser particles. Phosphor layers composed of such blends can thus be more efficient at absorbing radiation, such as ultraviolet light. Lamps according to embodiments of the present disclosure can thus use rare earth phosphors more efficiently (and thus at lower cost). This effect may be due to the fact that the phosphor particles pack more efficiently due to the presence of multiple particle sizes in the coating.

According to embodiments of the present disclosure, the phosphor blend may include a red emitting rare earth phosphor. Such a red-emitting rare earth phosphor may be a multimodal rare earth phosphor, although the present invention is not limited thereto.

Rare earth phosphors that emit red light may include one or more of the following: europium-doped yttrium oxide (eg, YEO), europium-doped yttrium vanadium phosphate (eg, Y(P,V)O ₄ :Eu), manganese Metal pentaborates co-activated with cerium (such as CBM), etc. Other possible red rare-earth phosphors could include Eu-activated yttrium oxysulfide, or europium(III)-doped gadolinium oxide and gadolinium borate, such as (Y,Gd)2O3:Eu3+ and (Y,Gd)BO3:Eu3+. A possible formula for europium-doped yttrium oxide phosphors may typically be (Y(1-x)Eux)2O3, where 0<x<0.1, possibly 0.02<x<0.07, eg x=0.06. Such europium-doped yttrium oxide phosphors are often abbreviated as YEO (or sometimes YOX or YOE). A possible manganese and cerium co-activated metal pentaborate may have the formula (Gd(Zn,Mg)B ₅ O ₁₀ : Ce ³⁺ , Mn ²⁺ (CBM).

According to embodiments of the present disclosure, the phosphor blend may include a green emitting rare earth phosphor. Such a green-emitting rare earth phosphor may be a multimodal rare earth phosphor, although the present invention is not limited thereto. Green-emitting rare earth phosphors may include one or more of the following: lanthanum phosphate co-activated with cerium and terbium (e.g. LAP), magnesium aluminate co-activated with cerium and terbium (e.g. CAT), or europium and manganese co-activated Barium magnesium aluminate (such as BAMn), or cerium and terbium co-activated gadolinium magnesium pentaborate (such as CBT, GbMgB ₅ O ₁₀ : Ce ³⁺ , Tb ³⁺ ), etc. A typical formula of lanthanum phosphate doped with cerium and terbium may include one selected from: LaPO ₄ : Ce, Tb, LaPO ₄ : Ce ³⁺ , Tb ³⁺ , or (La, Ce, Tb)PO ₄ . Certain cerium and terbium doped lanthanum phosphate phosphors according to embodiments of the invention may have the formula (La _{(1-xy) CexTby ) PO4} , where 0.1<x<0.6 and 0<y<0.25( Or possibly, 0.2<x<0.4, 0.1<y<0.2) (LAP). Other cerium and terbium doped phosphors may be (Ce,Tb)MgAl ₁₁ O ₁₉ (CAT) and (Ce,Tb)(Mg,Mn)Al ₁₁ O ₁₉ . Depending on the molar ratio in its activator, BAMn may be considered as a green rare-earth phosphor.

According to embodiments of the present disclosure, the phosphor blend may include a blue light emitting rare earth phosphor. Such a blue emitting rare earth phosphor may be a multimodal rare earth phosphor. Rare earth phosphors that emit blue light may include one or more of the following: europium-doped halophosphates (such as SECA, which has the typical formula (Sr,Ca,Ba) ₅ (PO ₄ ) ₃ Cl:Eu ²⁺ ), europium-doped barium magnesium aluminate (e.g. BAM), europium-manganese co-activated magnesium aluminate (e.g. BAMn), europium-doped strontium aluminate (e.g. SAE), europium-doped borophosphate, Cerium-doped yttrium aluminate (such as YAG) and the like. Strontium aluminate doped with europium may have the formula Sr ₄ Al ₁₄ O ₂₅ :Eu ²⁺ (SAE). In the formula, the europium-doped strontium aluminate phosphor may comprise Sr and Eu in the following atomic ratio: Sr _0.90-0.99 Eu _0.01-01 . BAM may have the formula (Ba,Sr,Ca)MgAl ₁₀ O ₁₇ :Eu ²⁺ . BAMn may have the formula (Ba,Sr,Ca)MgAl ₁₀ O ₁₇ :Eu ²⁺ ,Mn ²⁺ . Europium and manganese co-activated barium magnesium aluminate (eg BAMn) can sometimes be considered a blue-green, blue or green rare earth phosphor, usually depending on the molar ratio in its activator.

As previously mentioned, phosphor blends according to embodiments of the present invention may also optionally include non-rare earth activated phosphors, such as halide phosphors. As used in this specification, the term "halogenated phosphor" is intended to mean a phosphor comprising at least one halogen component, preferably chlorine or fluorine or mixtures thereof, but which is not activated by rare earth elements. Halophosphors can emit colored light when excited, or can emit light that is perceived as white. Examples of halophosphors that emit blue or blue-green light may include calcium halophosphates (eg, calcium fluorophosphates) activated by antimony (3+). Examples of halophosphors that emit white light may include calcium fluorochlorophosphates activated by antimony (3+) and manganese (2+), such as Ca _5-xy (PO ₄ ) ₃ F _1-zy Cl _z O _y : Mn _x Sb _y . Other non-rare earth activated phosphors may include one of strontium red (eg (Sr,Mg) ₃ (PO ₄ ) ₂ :Sn) or strontium blue (eg Sr ₁₀ (PO ₄ ) ₆ F ₂ :Sb,Mn) or more.

When describing the chemical formula of a phosphor, one or more elements following the colon represent one or more activators. If two or more elements are present after the colon, they are usually both present as activators. As used throughout the context of the present invention, the term "doped" is equivalent to the term "activated". Various phosphors of any color described in this specification may have different elements enclosed in parentheses and separated by commas, as in (Ba,Sr,Ca)MgAl ₁₀ O ₁₇ :Eu ²⁺ ,Mn ²⁺ phosphors . As can be understood by those skilled in the art, the symbol (A,B,C) represents (A _{x By} C _z ), where 0≤x≤1, 0≤y≤1, 0≤z≤1 and x+y+z =1. For example, (Sr, Ca, Ba) represents (Sr _x Ca _y Ba _z ), where 0≤x≤1, 0≤y≤1, 0≤z≤1 and x+y+z=1. Usually, but not always, x, y, and z are all non-zero. The notation (A,B) denotes (A _x B _y ), where 0≤x≤1, 0≤y≤1 and x+y=1. Usually, but not always, both x and y are non-zero.

Blue phosphors can have a peak emission at about 440 to 500 nm; green phosphors can have a peak emission at about 500 to 600 nm; and red phosphors can have a peak emission at about 610 to 670 nm (for some red phosphors, there may be one or more peaks down to 590nm).

According to an embodiment of the invention, the lamp includes one or more radiation sources, which may include one or more of a discharge based radiation source or a solid state radiation source. Discharge-based radiation sources may include low-pressure vapor discharge sources, such as are used in fluorescent lighting systems. Radiation sources may also include solid state radiation sources, such as OLEDs or LEDs. For example, certain solid state radiation sources, such as LEDs or OLEDs, can emit electromagnetic radiation that can be converted into usable light of a different wavelength, such as visible light, using phosphor blends. To generate visible (eg white) light using a blue or UV solid state radiation source (eg LED die), the phosphor blend can be deposited directly on the solid state radiation source. A pre-formed tile of the phosphor blend can also be bonded on top of the LED die. It is also within this disclosure to combine the phosphor powder blend in an encapsulant or binder material such as silicone or epoxy and mold the mixture over a solid state radiation source such as an LED die to form lens. The blend can also be a remote phosphor configuration relative to the solid state radiation source.

In many embodiments of the invention, the lamp may be a low pressure discharge lamp (eg a fluorescent lamp). Such lamps generally comprise at least one light-transmissive envelope (which may be made of glass-like (e.g., glass) material and/or ceramic, or any suitable material that allows transmission of at least some visible light), sealed within said at least one light-transmissive envelope The filling gas composition (that is, the filling gas composition capable of sustaining a discharge), the phosphor blend of the present invention, and optionally one or Multiple electrical leads. Alternatively, such lamps may be electrodeless.

Low pressure discharge lamps may generally be constructed by any effective method, including many known or conventional methods. Some non-limiting examples of materials that may constitute the discharge fill of the lamp include at least one material selected from the group consisting of Hg, Na, Zn, Mn, Ni, Cu, Al, Ga, In, Tl, Sn, Pb, Bi, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W, Re, Os, Ne, Ar, He, Kr, Xe and their combinations and compounds, etc. In one embodiment, the discharge fill material in the lamp comprises mercury. In another embodiment, the discharge fill material in the lamp does not contain mercury. In particular, when a substantially mercury-free discharge filling is required, the discharge filling may contain at least one material selected from the group consisting of gallium halide, zinc halide, indium halide, and the like. The fill is present at any effective pressure, such as a pressure effective to maintain a low pressure discharge, as can be readily determined by any person skilled in the art. Some suitable pressures may include a total fill pressure of about 0.1 to about 30 kPa, with other values also possible.

It is within the scope of the present disclosure to make and use various types of lamps disclosed in this specification, including mercury fluorescent lamps, low dose mercury, very high output fluorescent lamps, and mercury-free low pressure fluorescent lamps. The lamp may comprise electrodes or may be electrodeless. The lamp can be linear, but any size shape or cross-section can be used. It can be of different types, any fluorescent lamp like T5, T8, T12, 17W, 20W, 25W, 32W, 49W, 54W, 56W, 59W, 70W, linear, circular, 2D, twin tube or U-shaped fluorescent lamp. They can be high efficiency or high output fluorescent lamps. For example, embodiments of the invention include lamps that are curved in shape, as well as compact fluorescent lamps that are generally known to those of ordinary skill in the art. Compact fluorescent lamps (CFLs) have a folded or wound topology such that the overall length of the lamp is much shorter than the unfolded length of the glass tube. Various manufacturing modes and configurations of linear and compact fluorescent lamps are generally known to those skilled in the art of low-pressure discharge lamps.

Typically, when used in a low-pressure discharge lamp, phosphor blends according to embodiments of the present invention will have at least one phosphor composition supported on a light-transmissive envelope, such as on an inner surface of the light-transmissive envelope . In embodiments where the lamp has multiple envelopes, the light transmissive envelope on which the phosphor composition is disposed may be an inner envelope. The phosphor composition can be applied to the envelope by any effective method, including known or conventional methods, such as by slurrying. Methods of preparing and applying phosphor coating slurries are generally known or conventional in the art.

When a phosphor blend according to embodiments of the invention is present as a layer disposed on the envelope of a discharge lamp, it may be present as a single layer, or as multiple layers of the same blend, or as a multilayer coating. Layers of layers exist. In general, a barrier layer can also be provided on the envelope of the discharge lamp.

Vapor discharge lamps according to embodiments of the invention may include 1 g to about 6 g of phosphor blend. For example, for a 4 foot T8 fluorescent lamp, about 1 g to about 4 g/bulb of phosphor blend can be used; for a 4 foot T12 fluorescent lamp, about 1 g to about 6 g/bulb of phosphor blend can be used. For an 8 foot lamp, a T8 lamp may use about 2g to about 8g, and a T12 lamp may use about 2g to about 12g. An alternative way of expressing the content of the phosphor blend is mass/surface area of the inner envelope. By this measure, the lamp may typically contain from about 1 mg/cm ² to about 6 mg/cm ² of the phosphor blend.

Referring now to FIG. 1 , the specification shows an exemplary embodiment of one type of lamp, a fluorescent lamp 1 , in accordance with the present disclosure. Such lamps may be low or high pressure and may contain mercury vapor as a fill, or may be mercury-free but (in this exemplary embodiment) contain discharge-supporting vapor. The fluorescent lamp 1 has a light-transmissive tube or envelope 6 formed of glass or other suitable material and which may have a circular cross-section. The inner surface (not particularly shown) of the glass envelope 6 is provided with a phosphor-containing layer 7 . A barrier layer may be present between the envelope 6 and the phosphor-containing layer 7 . The lamp is usually hermetically sealed by a substrate 2 attached respectively to the ends of the tube. Generally, two spaced electrodes 5 are respectively installed on the base 2 and can be supported by the stem 4 . The electrodes 5 are usually supplied with electrical current by a plug 3 housed in a power socket. A discharge sustaining filling 8, which may be formed from mercury and an inert gas, is sealed inside the glass tube. The inert gas is typically argon or a mixture of argon and other noble gases at low pressure which, in combination with a small amount of mercury, provides a low vapor pressure mode of operation.

The phosphor-containing layer 7 contains a blend of phosphor particles comprising at least one multimodal rare earth phosphor. The amount of individual phosphor materials used in the phosphor composition of the phosphor layer 7 will vary depending on the desired color spectrum and/or color temperature. The weight percent of each phosphor making up the phosphor layer 7 can vary depending on the characteristics of the desired light output.

Embodiments of the invention also include a method of making a lamp using a phosphor blend comprising at least two different rare earth phosphors. This method comprises at least the step of blending at least one multimodal rare earth phosphor comprising particles having a multimodal particle size distribution with a different rare earth phosphor. The lamp may be constructed by any effective method, which may include other steps generally known or conventional in the art.

There may also be embodiments of the invention in which the phosphor blend is used as or as part of a scintillation system. Typically, if the phosphor blend is used as a scintillator, it may be provided in the form of a transparent solid body. The phosphor blends disclosed in this specification are useful as part of gamma ray cameras, CT scanners, lasers, CRTs, plasma displays, and as precursors for scintillators.

Lamps according to embodiments of the invention may provide a number of advantages. For example, a lamp can achieve a greater lumen output than the same lamp (at an equal phosphor blend coat weight) in which the phosphor blend does not include at least one multimodal rare earth phosphor. Accordingly, embodiments of the present invention also include a method of obtaining consistent lumens at lower phosphor weights by converting radiation from phosphor blends (or in other words, a method for achieving lumens at the same phosphor weight method for obtaining higher lumens), wherein one of the plurality of phosphors in the blend (eg, a rare earth phosphor or a non-rare earth phosphor) has a multimodal particle size distribution. In this approach, the multimodal phosphor can be a rare earth phosphor or a halide phosphor.

In order to facilitate a further understanding of the present invention, the following examples are provided. These examples are illustrative and should not be construed as any kind of limitation on the scope of the invention.

example

Example 1

A blend of phosphors was prepared according to an example of the present invention using the following three rare earth phosphors: blue BAM, green LAP, and red YEO. BAM has a unimodal particle size distribution with a _d50 of 7.73 microns, while LAP has a unimodal particle size distribution with _ad50 of 5.27 microns. The YEO used was produced in such a way as to obtain a bimodal particle size distribution. It was formulated from small particle YEO (56 wt% of total red YEO) and large particle YEO (44 wt% of total red YEO). Relatively larger particles are obtained commercially, while relatively smaller particles can be obtained by firing co-precipitated yttrium/europium oxide. The particle size distributions for each of the multiple component phosphors are shown in Table I (measured on a LA-950 Horiba Laser Scattering PSD Analyzer).

Table I

The relative weight percentages of the component phosphors are shown in Table II.

Table II.

To facilitate coating, the blend is combined with a polymeric binder (PEO) and an inorganic additive (alumina). After suspension, the interior surface of a T8 linear fluorescent lamp was coated to adhere the phosphor to the bulb. The total weight of the phosphor blend used in this example was 1.5 g/bulb (about 1.5 mg/cm ² ). After completion of the T8 lamps, in the scope of spectrophotometric testing, the lumen output was measured by the following IES standard LM-9-09 (Electrical and Photometric Measurement of Fluorescent Lamps). In this example, the lumens per watt (LPW) according to the standard is 87.

Example 2

In this example, the same type of lamp was constructed under the same conditions as in Example 1, the only difference being the coating weight. In this example, the total weight of the phosphor blend used in this example was 2.0 g/bulb (approximately 2.1 mg/cm ² ). Measuring lumen output in the same way as the previous example gives 88LPW.

Comparative example 3

Comparative lamps were constructed from the same phosphors in the same relative proportions in the same manner as Examples 1 and 2, except that they did not have a bimodal particle size distribution. Only relatively large particle size YEO red light was used to make T8 lamps. That is, the PSD for YEO is the same as the "relatively large particle size" of Example 1. The weight percentages of YEO, LAP and BAM in the blend were 49.6 wt%, 41.1 wt% and 9.3 wt%, respectively. Coating this blend on a lamp at 1.5 g/bulb in the same manner as the example gave 84 LPW, and a coating of 2.0 g/bulb showed 86 LPW (measured in the same manner as the example). Therefore, the LPW value of the exemplary blend using the bimodal YEO red light is 2-3 lumens per watt higher than that of this comparative example.

Comparative example 4

A comparison lamp was constructed from the same phosphor in the same relative proportions as Examples 1 and 2, except that it did not have a bimodal particle size distribution, and only smaller particle size YEO red light was used. The PSD for YEO is the same as the "relatively small particle size" of Example 1. The weight percentages of YEO, LAP and BAM in the blend were 49.6 wt%, 41.1 wt% and 9.3 wt%, respectively. Applying this blend to a lamp at 1.5 g/bulb in the same manner as the example gave 83 LPW, and at 2.0 g/bulb showed 86 LPW (measured in the same manner as the example). Compared to this comparative example, the LPW value of the exemplary blend using bimodal YEO red light is 2-4 lumens per watt higher.

As used in this specification, approximate language may be used to modify any quantitative representation that may vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms (eg, "about" and "substantially") may not be limited to the precise value indicated in some cases. The modifier "about" used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context (eg, includes the degree of error associated with measurement of the particular quantity). "Optional" or "optionally" means that the subsequently described event or circumstance may or may not occur, or that the subsequently identified material may or may not be present, or that the description includes instances where there is, and instances where the event or circumstance does not occur or where the material does not exist. The singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise. All ranges disclosed in this specification include the stated endpoints and are independently combinable.

As used in this specification, the phrases "adapted to," "configured to," and the like mean an element that is sized, arranged, or manufactured to form a specified structure or to achieve a specified result. While the invention has been described in detail with respect to only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of changes, variations, substitutions or equivalent arrangements not described herein but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description. It is also contemplated that advances in science and technology will enable equivalents and substitutions not presently contemplated due to language imprecision, and where possible, such variations should also be construed to be covered.

Claims (20)

1. A lamp comprising: a radiation source capable of emitting electromagnetic radiation at a first wavelength; and a phosphor blend configured in combination with the radiation source for converting the electromagnetic radiation to a second wavelength, The phosphor blend comprises at least two different rare earth phosphors, wherein the phosphor blend comprises at least one multimodal rare earth phosphor. 2. The lamp of claim 1, wherein the at least one multimodal rare earth phosphor comprises a first population of relatively coarser particles and a second population of relatively finer particles. 3. The lamp of claim 2, wherein said first group comprises from about 20 to about 80 wt% of said at least one multimodal rare earth phosphor, and said second group comprises said From about 80 to about 20 wt% of at least one multimodal rare earth phosphor. 4. The lamp of claim 2, wherein the multimodal rare earth phosphor comprises a bimodal particle distribution having a relatively coarser particle size corresponding to _ad50 less than or equal to about 10 microns A first maximum for particles, and a second maximum for relatively finer particles having _ad50 greater than or equal to about 1 micron. 5. The lamp of claim 1, wherein the blend comprises two or more different multimodal rare earth phosphors. 6. The lamp of claim 1, wherein the blend comprises at least three different rare earth phosphors. 7. The lamp of claim 1, wherein the blend further comprises at least one halophosphor. 8. The lamp of claim 1 , wherein compared to an identical lamp at an equal phosphor coat weight in which the blend does not comprise at least one multimodal rare earth phosphor, the The above-mentioned lamps get more lumens. 9. The lamp of claim 1, wherein the at least one multimodal rare earth phosphor comprises a plurality of particles, wherein at least some of the relatively finer particles are sized to fit at least some of the relatively coarser particles gap between. 10. The lamp of claim 1, wherein the blend comprises a red emitting multimodal rare earth phosphor. 11. The lamp of claim 10, wherein the red-emitting rare earth phosphor comprises europium-doped yttrium oxide, europium-doped yttrium vanadium phosphate, or manganese and cerium co-activated metal pentaboron one or more of salts. 12. The lamp of claim 1, wherein the blend comprises a green emitting multimodal rare earth phosphor. 13. The lamp of claim 12, wherein the green emitting rare earth phosphor comprises lanthanum phosphate co-activated with cerium and terbium, barium magnesium aluminate co-activated with europium and manganese, co-activated with cerium and terbium One or more of magnesium gadolinium pentaborate, or magnesium aluminate coactivated by cerium and terbium. 14. The lamp of claim 1, wherein the blend comprises a blue emitting multimodal rare earth phosphor. 15. The lamp of claim 14, wherein the blue emitting rare earth phosphor comprises europium doped halophosphate, europium doped barium magnesium aluminate, europium and manganese coactivated barium aluminate One or more of magnesium, europium-doped strontium aluminate, europium-doped borophosphate, cerium-doped yttrium aluminate, or SECA. 16. The lamp of claim 1, wherein the lamp comprises 1 mg/ ^cm2 to about 6 mg/ ^cm2 of the phosphor blend. 17. The lamp of claim 1, wherein the radiation source comprises one or more of a discharge based radiation source or a solid state radiation source. 18. The lamp of claim 1, wherein said first wavelength is in the blue or UV region of the electromagnetic spectrum, and said second wavelength is in the visible region of the electromagnetic spectrum and is shorter than said The first wavelength is longer. 19. A low pressure discharge lamp comprising: at least one light-transmitting envelope; a gas filling composition capable of sustaining a sealed electrical discharge within said at least one light transmissive envelope; and A phosphor blend; wherein the phosphor blend comprises at least two different rare earth phosphors, wherein the phosphor blend comprises at least one multimodal rare earth phosphor. 20. A method comprising the steps of, combining a radiation source capable of emitting electromagnetic radiation at a first wavelength with the phosphor blend to convert the electromagnetic radiation to a second wavelength; wherein the phosphor blend comprises at least two different rare earth phosphors, and wherein the phosphor blend comprises at least one multimodal rare earth phosphor; Therein, the method operates the lamp to obtain a consistent lumen output at a reduced amount of phosphor, and/or the method operates the lamp to obtain a higher lumen output at a constant amount of phosphor.